Fix symbol list for mangled Mesa on Darwin.

Fix symbol list for mangled Mesa on Darwin.

When building mangled Mesa on Darwin, the exported symbols are
named `_mgluWhatever' instead of simply `_gluWhatever'.  When
using a list of exported symbols via the system ld's
`-exported_symbols_list' command line option (as done by mklib),
this resulted in error messages about exporting symbols which do
not exist.

Fortunately the file format accepts simple wildcards.  This throws
a wildcard so that the symbol list will match both the mangled and
non-mangled names, preventing the warning and actually exporting
the correct symbols in one shot.